Such a capsule is disclosed e.g. in U.S. Pat. No. 5,195,142, which claims priority from the Italian patent applications for Utility Model No. 21175/90 and 21176/90 filed by the Applicant, which could be referred to for further details.
Therein the case made from insulating material acts as a container for the other members and it is provided on its perforated wall with an annular housing extending coaxially thereto, with a reference tooth designed to engage in a corresponding notch provided on the spool to assure the correct positioning of the latter during the assembly of the capsule, and with an annular extension designed to snap on external face of the spool and secure it.
This type of capsule as disclosed in the above-mentioned application, when positioned in the corresponding seat of the handset requires a further gasket for seal.
In an advantageous embodiment also described and illustrated in the above-mentioned U.S. patent, the case is formed directly on the bottom of the handset housing by pressing. In this circumstance the additional gasket is no longer necessary, but the automation of the capsule assembly is affected since the relative operations are tied to the type of the handset.